In many instances it is necessary to heat a cellulose pulp for various purposes, such as to initiate and/or to continue different chemical reactions and treatments. This applies, for example, to many bleaching steps. In order to ensure this heating, steam of different pressures is generally used, depending upon the pressure level required by the process in the particular installation in question.
Heating of the pulp with steam preferably takes place in a pipe which is conveying the pulp to the treatment step in question. The pulp concentration can be from about 3 to 20%, and preferably from about 5 to 15%. In this manner, a relatively rapid and uniform heating of the pulp can be achieved. The steam is normally supplied through one or more steam pipes which are connected to the pulp pipe. Such so-called steam extension pipes connected to the pipe system can be designed in various ways, whereby the resultant temperature increase of the pulp can vary, and the functioning of subsequent machines will be more or less efficient.
In earlier systems or arrangements, problems have often arisen in view of the development of large steam bubbles on the inside of the pulp pipe. When these steam bubbles rapidly condense, condensate stresses and bangs occur, which cause harmful cavitations both in the pipe system itself and in surrounding components. Furthermore, it is difficult to achieve an entirely uniform temperature profile in the pulp. It is certainly possible to improve the temperature profile by inserting the steam pipes into the pulp pipe, but doing so will cause a considerable deterioration in the flow within the pulp pipe, as well as difficulties in cleaning the pulp pipe and steam pipes in case of plugging.
The aforesaid problems are solved by the present invention. As a result of this invention, the steam heating can take place effectively and uniformly since the steam is exposed to a large volume/surface of the passing pulp flow. Furthermore, the steam is supplied without any condensate bangs and without interfering with the pulp flow. The arrangement according to the present invention is also designed so that it can be easily cleaned when plugging of pulp takes place.